Structural sandwich plate members

ABSTRACT

A structural sandwich plate member, comprising first and second face plates and a plastics or polymer core bonding said face plates together with sufficient strength to transfer shear forces therebetween, said face plates being formed of a non-metal reinforced composite material.

CROSS REFERENCE TO RELATED APPLICATION

This is a U.S. national phase application under 35 U.S.C. §371 ofInternational Patent Application No. PCT/GB03/00225 filed Jan. 17, 2003,and claims the benefit of Great Britian Patent No. 0201903.2 filed Jan.28, 2002 which is incorporated by reference herein. The InternationalApplication was published in English on Aug. 7, 2003 as WO 03/064154 A1under PCT article 21(2).

FIELD OF THE INVENTION

The present invention relates to structural sandwich plate members,which plate members comprise outer plates bonded together by a corelayer of plastics or polymer material which transfers shear forcestherebetween, and to structures formed by connecting together structuralsandwich plate members.

BACKGROUND INFORMATION

Structural sandwich plate members, known commercially as SPS™, aredescribed in U.S. Pat. No. 5,778,813, British Patent Application GB-A-2337 022 and International Application No. GB00/04198 which documents areincorporated herein by reference. Such structural sandwich plate memberscomprise outer metal plates bonded together by a plastics or polymercore with sufficient strength to transfer shear forces therebetween. Theplastics or polymer core may be solid and continuous, occupying theentire volume between the outer metal plates, or may be interrupted by,e.g. foam, forms which leave continuous plastics or polymer connectionsbetween the outer metal plates. A principal use of these structuralsandwich plate members is to replace stiffened steel structures, e.g. inmaritime, offshore and civil engineering applications. In suchapplications, the structural sandwich plate members enable theelimination of some or all stiffening elements providing a simplerstructure that is easier to construct and maintain. In particular, theamount of welding necessary is generally substantially reduced ascompared to a conventional stiffened steel structure.

A further advantage of such structural sandwich plate members is thatthey can be prefabricated, either as individual plate members or as morecomplex modules to be assembled into the eventual structure.Pre-fabricated modules can be made under factory conditions to greateraccuracy than traditional structures, can be assembled on site andfurther ease construction.

SUMMARY OF THE INVENTION

Although such structural sandwich plate members have considerabletechnical and economic advantages over traditional stiffened steelstructures, their weight is comparable to, or moderately less than thatof traditional stiffened steel structures and a considerable amount ofsteel or metal is still present, which can be undesirable in someapplications.

It is an aim of the present invention to provide alternative forms ofstructural sandwich plate members, preferably with lower weight thanthose made with all metal face plates and having other improvedproperties.

According to the present invention, there is provided a structuralsandwich plate member, comprising first and second face plates and aplastics or polymer core bonding said face plates together withsufficient strength to transfer shear forces therebetween, at least oneof said face plates being formed of a non-metal reinforced composite orreinforced polymer material.

A structural sandwich member with one non-metal face plate can provideimproved chemical resistance and is advantageous for use in formingstorage tanks, with the non-metal face plate on the inside. If both faceplates are made of non-metal material, a metal free structure, havingreduced electromagnetic signature can be made.

The non-metal face plates are preferably made of a fiber-reinforcedpolymer material such as carbon-fiber reinforced polymer material. Thestrengths and like properties of such composite materials are oftenspecified as a ratio whereby the value of the property in other units isdivided by the density of the material. In the invention, the strengthratio of the face plates (tensile strength/density) is preferably in therange of from 0.03 to 0.5, most preferably 0.1 to 0.25 (MPa/kgm⁻³).Similarly, the stiffness ratio (modulus of elasticity/density) ispreferably in the range of 0.5 to 50, most preferably 2 to 26(MPa/kgm⁻³).

The structural sandwich plate members according to the invention areparticularly advantageous for use in applications where extremely lowweight is required or steel and other metals are undesirable. Forexample, the structural sandwich plate members according to theinvention may be used in mine sweepers and other specialist militaryvessels for which a low electromagnetic signature or a reduction inship/structure borne noise is desirable. Civil engineering applicationsfor the invention include bridge deck panels and chemical tanks. Forbridge deck panels, the weight savings can provide a substantialreduction in the cost of the superstructure supporting the deck and thenon-metal face plates provide a structure that is resistant to corrosiveroad salts. For chemical storage tanks, one or both face plates can bemade of a material chosen to resist chemical attack from the storedchemical.

The present invention also provides structures comprising at least onestructural sandwich plate member as described above.

Further, the present invention provides a method of manufacturing acomponent of a structure comprising the steps of:

-   -   providing first and second face plates in a spaced apart        relationship to define a cavity, at least one of said first and        second face plates being formed of a non-metal reinforced        composite material and    -   injecting plastics or polymer material into said cavity to bond        said first and second face plates together with sufficient        strength to transfer shear forces therebetween.

Yet further, the present invention provides a method of reinforcing anexisting metal structure comprising the steps of:

-   -   providing a reinforcing layer on said metal structure in spaced        apart relation to thereby form at least one cavity between inner        surfaces of said metal structure and said reinforcing layer;    -   injecting an intermediate layer comprised of an uncured plastics        or polymer material into said cavity; and    -   curing said plastics material so that it adheres to said inner        surfaces of said metal structure and said reinforcing layer;        wherein    -   said reinforcing metal layer is formed of a non-metal reinforced        composite or reinforced polymer material.

This method can be used for the repair or rehabilitation of an existingmetal, e.g steel, structure that has deteriorated due to age, corrosionor wear. The reinforcing layer reinstates the structural capacity of theexisting structure and inhibits further deterioration. The light weightreinforcing layer may be shaped or formed off-site or in-side to fit theshape of the existing structure, including any reinforcing elements. Thereinforcing layer may be made of, or include, a layer of ceramicmaterial to provide enhanced fire resistance. The method of the presentinvention can be applied simply in confined or dangerous areas, e.g. theinterior of storage tanks, using prefabricated sections to avoid hotwork on site.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described below with reference tothe following description of exemplary embodiments and the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view of a structural sandwich plate memberaccording to a first embodiment of the present invention;

FIG. 2 is cross-sectional view of a structural sandwich plate memberaccording to a second embodiment of the present invention;

FIG. 3 is a cross-sectional view illustrating a method of joining twostructural sandwich plate members according to the invention; and

FIG. 4 is a cross-sectional view of a structural sandwich plate memberaccording to a third embodiment of the invention;

FIG. 5 is a partly sectional perspective view of a structure reinforcedusing a method according to a fourth embodiment;

FIG. 6 is a cross-sectional view of the structure of FIG. 5;

FIG. 7 is a cross-sectional view of the structure of FIG. 6 along lineA-A.

In the drawings, like parts are indicated by like references.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in cross-section a structural sandwich plate member 1according to a first embodiment of the present invention.

The structural sandwich plate member 1 comprises outer face plates 11and 13 which are bonded together by core 12. The face plates 11, 13 aremade of a carbon-fiber reinforced plastics material whilst the core 12is made of a plastics or polymer material such as polyurethane. The core12 is preferably compact, i.e. not foamed, though a certain amount ofcavitation may be permitted in some applications. The core 12 isintegrally bonded to the face plates 11, 13 providing continuous supportand sufficient shear and bond strength to transmit the expected shearloads between them. The thicknesses of the sandwich elements 11, 12, 13are selected to provide the flexural and in-plane strength and stiffnessof the sandwich plate for the particular static and dynamic requirementsThe strength and stiffness ratios for the non-metal reinforced compositeplates are expressed as the ratio of the tensile strength divided by themass density; and the ratio of the modulus of elasticity divided by themass density and are in the range of 0.03 to 0.95, preferably 0.1 to0.25 (MPa/kgm⁻³); and 0.5 to 50, preferably 2 to 26 (MPa/kgm⁻³)respectively, for use in maritime, offshore and civil engineeringstructures. It will be appreciated that the dimensions of the memberwill vary according to application but for practical maritime and civilengineering applications the face plates may have thicknesses T₁, T₃ inthe range of from 1 to 30 mm and the core a thickness T₂ in the range offrom 10 mm to 150 mm. The thicknesses of the two face plates may bedifferent and may vary across their area. Similarly, the thickness ofthe core may vary across the area of the plate member. Although theplate member 1 is shown in FIG. 1 as being flat it may be curved or havea more complex contour as desired for a specific application.

In a second embodiment of the invention, a structural sandwich platemember 1 a shown in cross section in FIG. 2 may be provided withadditional elements embedded in the core 12 to reduce weight or increasestrength. Otherwise, the structural sandwich plate member of the secondembodiment is the same as that of the first embodiment. For example,FIG. 2 shows a solid foam form 15 which has a lower density than thematerial of the core 12 and so reduces weight of the structural sandwichplate member. Alternatively, hollow form 16 may be used for the samepurpose; such forms may comprise elongate extruded plastics pipes orprefabricated hollow foam forms and may have other profiles than asillustrated in FIG. 2. The hollow form 16 may be manufactured as a wideraft or in sections that connect together to form such rafts. The foamforms 15 and hollow forms 16 are positioned within the core so thatcontinuous paths of the core material 12 connect the face plates 11, 13together. Preferably, the foam or hollow forms 15, 16 leave continuouselastomer ribs extending between the face plates 11, 13. Solid or hollowfoam or hollow forms may be layered, aligned, placed orthogonally or atany preferred orientation with respect to one another to maximizestructural performance.

To increase the strength of the element, transverse shear plates 17extending between the face plates 11, 13 may also be provided. Suchshear plates are preferably perforated to improve bonding between thecore 12 and the shear plates 17. The shear plates 17 assist in transferof shear forces between face plates 11, 13.

To manufacture the structural sandwich plate member according to theinvention, the face plates 11, 13 are placed in a spaced apartrelationship, either in a mold or with edge members (not shown) spanningbetween them, to form a closed cavity. The cavity is then injected withmaterial to form the core 12. Of course, internal elements such as thoseshown in FIG. 2 are placed in the mold prior to closing or on one of theface plates before the edge members are attached to form the closedcavity. The core material when setting acts to bond together the faceplates to form a composite structural unit. The required bond ispreferably formed through the natural adhesiveness between the corematerial and the face plates 11, 13 but, if desired, additionaladhesives or surface preparations of the face plates 11, 13 or internal(wire) mesh placed parallel to the interior plate surfaces may beemployed.

As shown in FIG. 3, to form complex structures, structural sandwichplate members 1 b, 1 c may be joined by providing a prefabricated edgemember 19 on one structural sandwich plate member 16 that projects and asimilar edge member 19 on the other that is recessed so that the twostructural sandwich plate members interlock. A layer of suitableadhesive 18 is provided between the mating parts.

FIG. 4 shows a structural sandwich plate member 30 according to a thirdembodiment of the invention. In this embodiment, the complete outershell is pultruded as an integral form, including additional details.

As seen in FIG. 4, the outer shell of the structural sandwich platemember 30 comprises face plates 31, 32, end walls 34, 36 and an internalstiffening rib 35. Aligned with end wall 36, an external stiffeninggirder 37 is provided. To facilitate connections between members 30, oneend has a portion of reduced thickness 39 forming a male member thatmates with a socket defined by flanges 38 on the other end. To completethe bond, adhesive is provided in the mating surfaces.

The members 30 are prefabricated off-site in long lengths, then cut asnecessary and shipped to the construction site. On-site they areassembled into the desired structure, which may involve furthertrimming, and once in place, plastics or polymer is injected to form thecore 12. In this way, dimensional accuracy can be assured by off-sitemanufacture and handling is facilitated on-site because the members arevery light and easy to cut before the core 12 is injected. When the coreis injected, the members achieve full structural strength.

FIGS. 5, 6, and 7 show a fourth embodiment of the present invention inwhich overlay 2 is added to repair an existing metal structure.

In FIGS. 5, 6 and 7, the bottom plate of a transfer or storage tanker isshown at 21 and is reinforced by bulb flats 22, 23 and girders 28. Suchbottom plates often become pitted overtime, necessitating repair orreplacement. This has conventionally been done by cutting out thecorroded plate section or reinforcement and welding in a replacement oradding additional plating over the corroded part. Where the tank ortanker has been used to store inflammable products, it is essential toflush out all residual vapours from the compartment in which such hotwork is to be done, and also all neighbouring compartments. This is timeconsuming and expensive.

According to the invention, a reinforcing layer 24, 25 is positioned ina spaced apart relationship to the plate to be repaired, in this casebottom plate 21. Spaces, such as elastomer stubs, may be used to ensurethe desired spacing. The reinforcing layer is made of a reinforcedcomposite or reinforced polymer material as in the previous embodiments.It may be provided in prefabricated sections of standard forms, orcontinual sections for a specific job, which are fitted around thereinforcing elements 22, 23, 28. In the present example, the bulb flats22, 23, are enclosed by the reinforcing layer but the girders 28 projectthrough, Sections 24, 25 of the reinforcing layer make rolled lap jointsto the girder 28. Where necessary, the sections can be cut to size witha jig-saw and can be joined by suitable adhesive or by bolting 26 to abulb flat.

Once the reinforcing layer 24, 25 has been completed, plastics orpolymer material is injected into the casing between reinforcing layer24, 25 and plate 21 and cured to form core layer 27. The core layer 27bonds the reinforcing layer and plate 21 together with sufficientstrength to transfer shear forces expected in use and thus forms acomposite structural whole.

With this invention, no significant heat is generated during the repairprocess so that only the compartment being worked in, and notneighbouring compartments, needs to be flushed of flammable vapours.

The method can also be applied to pipelines using molded or pultrudedoverlay sections with snap interlocking longitudinal seams andprefabricated ring perimeter sections.

Whilst embodiments of the present invention and possible uses for themhave been described, it will be appreciated that the connecting memberof the present invention may be constructed differently than asdescribed and may be used in other ways, as will occur to the skilledreader. The present invention is not to be limited save within the scopeof the appended claims.

1-21. (canceled)
 22. A structural sandwich plate member, comprisingfirst and second face plates and a plastics or polymer core bonding saidface plates together with sufficient strength to transfer shear forcestherebetween, at least one of said face plates being formed of anon-metal reinforced composite or reinforced polymer material.
 23. Amember according to claim 22 wherein said reinforced composite materialis a fiber-reinforced polymer material
 24. A member according to claim23 wherein said polymer material is reinforced with carbon fiber.
 25. Amember according to claim 22 wherein said face plates have strengthratios in the range of from 0.03 to 0.5, preferably 0.1 to 0.25(MPa/kgm⁻³).
 26. A member according to claim 22 wherein said face placeshave stiffness ratios in the range of from 0.5 to 50, preferably 2 to 26(MPa/kgm⁻³).
 27. A member according to claim 22 wherein said core isformed of thermosetting material, such as a polyurethane material.
 28. Amember according to claim 22 wherein said core is compact.
 29. A memberaccording to claim 22 wherein said face plates have a thickness in therange of from 1 mm to 30 mm.
 30. A member according to claim 22 whereinsaid core has a thickness in the range of from 10 mm to 150 mm.
 31. Amember according to claim 22 wherein said face plates and side wallsspanning between said face plates are pultruded as a single unit.
 32. Amaritime structure, ship, or boat having a hull constructed from atleast one structural sandwich plate member according to claim
 22. 33. Abridge deck panel comprising at least one structural sandwich platemember according to claim
 22. 34. A storage tank comprising at least onestructural sandwich plate member according to claim
 22. 35. A method ofmanufacturing a component of a structure comprising the steps of:providing first and second face plates in a spaced apart relationship todefine a cavity, said first and second face plates being formed of anon-metal reinforced composite material; and injecting plastics orpolymer material into said cavity to bond said first and second faceplates together with sufficient strength to transfer shear forcestherebetween.
 36. A method of building a structure comprising the stepsof: manufacturing a plurality of structural components according to themethod of claim 35; and assembling said structural components to formsaid structure.
 37. A method according to claim 36 wherein said steps ofmanufacturing and assembling are carried out at different sites.
 38. Amethod of reinforcing an existing metal structure comprising the stepsof: providing a reinforcing layer on said metal structure in spacedapart relation to thereby form at least one cavity between innersurfaces of said metal structure and said reinforcing layer; injectingan intermediate layer comprised of an uncured plastics or polymermaterial into said at least one cavity; and curing said plasticsmaterial so that it adheres to said inner surfaces of said metalstructure and said reinforcing layer; wherein said reinforcing layer isformed of a non-metal reinforced composite or reinforced polymermaterial.
 39. A method according to claim 38 wherein said existing metalstructure is a metal panel that is supported by beams, girders, or bulbflats and said reinforcing layer is arranged such that at least some ofsaid beams, girders, or bulb flats are positioned between said metalpanel and said reinforcing layer.
 40. A method according to claim 39wherein said reinforcing layer is bent such that said reinforcing layeris further from said metal panel in the proximity of said beams or bulbflats than in other positions.
 41. A method according to claim 38wherein said existing metal structure is a metal panel reinforced by atleast one girder, wherein said reinforcing layer is provided so that anedge thereof is jointed to said girder by a rolled lap joint.
 42. Amethod according to claim 35 wherein said structure is a building, abridge, a ship, a ship component, or an off-shore structure.
 43. Amethod according to claim 38 wherein said structure is a building, abridge, a ship, a ship component, or an off-shore structure.